The use of doppler radar techniques for measuring the speed of moving objects and more particularly for measuring the speed of motor vehicles is well known in the art. By their nature, doppler return signals are often very inaccurate. This is due to the large noise level that would include white noise, reflection difficulties due to multiple targets and/or the dropping of pulses at critical intervals so that incorrect and erroneous displays are prevalent in many prior art devices. A general solution to these prior art difficulties is given and described in the U.S. Patent to Berry, No. 3,689,921, issued Sept. 5, 1972, which is incorporated by reference herein.
It has become apparent that the efficiency of selective electronic speed limit law enforcement can be increased if the radar platform, conventionally a police patrol car, is capable of movement during such enforcement and surveillance. A number of devices also are known in the art which attempt to impart movement capabilities to the radar platform. While these devices work well for their intended purposes, they often are inaccurate or are dependent, in generating a speed solution, on factors other than the mere reflected return of a generated frequency. When the radar platform is moving, at least two doppler return signals are produced simultaneously and these signals create a complex wave form for the radar receiver input. One larger doppler signal component will be generated by the reflected waves from the road and the other stationary objects, with its frequency representing the speed of the radar platform. A second doppler signal component is generated by the waves reflected from an approaching vehicle, and since the relative speed between the approaching vehicle and the patrol car is the sum of their two ground speeds, this doppler signal component frequency will represent the sum of two ground speeds. It should be noted that the second doppler signal component's frequency always will be higher than the first if the patrol car and the moving vehicle are traveling in opposite directions. The radar unit of this invention isolates these two doppler signal components by selective filtering. Alternatively, two separate antenna systems could be used thereby with one antenna directed to the surface while the second system is directed to the oncoming target vehicle. The unit counts the two frequencies digitally, subtracts the speed of the radar platform from the doppler count of the approaching vehicle, and automatically converts the resultant digital count into mile per hour units. The result is the true ground speed of the approaching vehicle.
In the stationary mode of operation, only one predominant doppler signal is returned, which represents the speed of the approaching vehicle. The filtering process is bypassed and the doppler signal frequency is counted directly. The subtraction process is not executed since the radar platform speed is zero and the counted doppler frequency represents the speed of the approaching vehicle.
If a plurality of valid comparisons are indicated over a preselected number of counting cycles, the speed indicated by the totalized number of pulses is presumed valid and is accordingly digitally displayed or utilized to give either a visual or audible warning, thereby indicating a speed violation. If a non-concidence counter is activated, the count previously stored for possible display purposes is discarded and the counting and count comparison scheme must be recycled. In this manner, all false signals including noise and reflections are disregarded and only valid speed indications are chosen for display.
A primary objective of this invention is to provide a unique method and apparatus for use in law enforcement and vehicle speed surveillance systems that measure the speed of an approaching vehicle when the radar platform is moving.
Another object of this invention is to provide a radar unit of the character described that provides accurate speed measurement and a direct reading of the absolute speed of a target vehicle when the radar platform is moving.
A further object of this invention is to provide a unique doppler radar unit that validates the accuracy of a received doppler signal prior to indicating the count value of the same as a correlation to vehicle speed.
A further object of this invention is to provide a radar unit having a comparing circuit means which will activate an audible alarm if the indicated vehicle speed equals or exceeds a preset violation speed limit selectively programmed by the radar operator.
Yet another object of this invention is to provide a doppler radar unit that efficaciously generates a speed solution directly from reflected waves when both the radar platform and target vehicles are moving.
Another object of the invention is to provide a unique radar unit that produces a digital speed readout when both the radar platform and the target vehicles are moving and to obviate the need for any mechanical linkage with the vehicle acting as the radar platform. In this manner no connection with the host vehicle odometer is needed.
A further object is to provide a moving vehicle radar system of the character described that requires but one antenna system.
Another object of the invention is to provide a unique circuitry in a moving radar of the character described that utilizes a single time base with at least two received doppler signal components. In this manner, the need for two or more time bases is therefore obviated.
A still further object of the invention is to provide a unique circuit for use with a moving radar which includes a means for ignoring the speed of an in-range oncoming vehicle under preselected conditions.
Other and further objects of this invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.